1. Field of the Invention
This invention relates to systems and methods for capturing and placing a cardiac assist device. More specifically, this invention relates to systems and methods for magnetically capturing, placing and securing a chronic heart failure passive restraint device around desired portions of a heart.
2. Prior Art
Heart failure syndrome is a highly debilitating and degenerative disorder resulting from damage to the heart muscle. The damage to the heart muscle may be caused by a number of conditions, including coronary artery disease, long standing hypertension, leaky heart valve(s), and infections.
Heart failure typically occurs when a weakened heart cannot pump an adequate amount of blood to meet the demands of the body's other organs and tissues. The defining characteristic in the progression of heart failure is that there is eventually a reduction of the heart's ability to meet the metabolic needs of the body.
Whatever the cause or source of damage, the heart's ability to pump adequate amounts of blood to support the body's needs is diminished, and the progressive deterioration of cardiac physiology and function begins. The inadequate supply of oxygen-rich blood often causes people with heart failure to experience shortness of breath and fatigue during even routine daily activities. As the condition progresses, the contraction rate of the heart increases in response to decreasing cardiac output. As a result, the chambers of the heart, particularly the ventricles of the heart, become increasingly enlarged as the heart tries to compensate for the inefficiencies. FIGS. 1a-1c show representative stages of progressive deterioration of a heart, wherein FIG. 1a shows a normal heart H with appropriately sized atrial chambers 1 and 2, and appropriately sized ventricular chambers 3 and 4, FIG. 1b shows slightly enlarged ventricular chambers 3 and 4, and FIG. 1c shows increasingly enlarged ventricular chambers 3 and 4. Ultimately, a complex process of damaging structural and functional changes to the heart results. Ventricular dilation results in thinning of the ventricular wall, which elevates the wall stress. This increase in wall stress leads to altered gene expression at the cellular level that results in attenuated adrenergic response, impaired myocyte function, cardiomyocyte hypertrophy, altered extracellular matrix production and cell death. This remodeling process continues as the body tries to continually compensate for ineffective pumping and eventually leads to heart failure.
The disease of heart failure is common, lethal, and expensive to treat. An estimated 5.1 million Americans have heart failure with approximately 500,000 new cases diagnosed each year. In 1999, an estimated $20.3 billion in directs costs were spent for the care of heart failure patients. Heart failure is also the most common cause of hospitalization for patients 65 years and older in the United States. The mortality rate is 50% at five years for patients diagnosed with heart failure, and to date, there are limited treatment alternatives available.
Certain cardiac disease treatment devices have been proposed to help alleviate the disease of heart failure. For example, U.S. Pat. No. 6,425,856 provides a cardiac constraint device comprised of a jacket made of biologically compatible material. The jacket is configured to surround a valvular annulus of the heart and at least the ventricular lower extremities of the heart. FIG. 1d illustrates how the jacket 20 may be positioned around the heart 10 to improve cardiac function. The jacket works on a passive, mechanical level to reduce periodic myocardial over-stretch and wall stress, and serves as a constant “reminder” to the heart of how it should perform. The jacket thus encourages down-regulation of increased local neurohormonal activity, and reduction or elimination of cardiomyocyte maladaptive gene expression. These actions may halt the progressive deterioration of the heart and may stimulate reverse remodeling of the heart. Once positioned as desired around the heart, the jacket 20 is sutured to the heart. Ideal positioning of the jacket around the heart has proved problematic, however, particularly where endoscopic tools and techniques are used.
An alternative procedure for surrounding a heart with a cardiac assist device proposes placing a rectangular sheet of mesh underneath the heart and then pulling corners of the mesh sheet up and around the heart. Each corner of the mesh sheet is provided with suture tethers that are pulled in a designated sequence in order to wrap the mesh sheet around the heart. The instruments used to grab the tethers of the mesh sheet are placed through different ports in the chest wall. Capturing and pulling the tethers securely in the desired sequence is time consuming however and prone to errors as the instruments used have limited maneuverability, and the tethers frequently pull free from the capturing instruments.
Therefore, a need exists for systems and methods that provide more reliable capture and placement of a cardiac implant or cardiac assist device about a heart.